Ocean bacteria may have shut off ancient global warming

WARMER WORLD The amount of carbon-containing matter falling to the deep ocean increased during an extraordinarily warm period around 56 million years ago, researchers argue. In this computer simulation of the oceans at the time, red indicates high levels of falling carbon-rich material and green indicates low amounts.

Z. Ma et al/Nature Geoscience 2014

Ocean-dwelling bacteria may have vacuumed up carbon and halted a period of extreme warmth some 56 million years ago, according to a study published April 13 in Nature Geoscience.

The finding suggests how Earth might once have rapidly reversed a runaway greenhouse effect. However, rapidity is relative: The bacteria would be far too slow to head off today’s human-caused climate impacts.

Scientists seeking to understand the present-day climate often study the Paleocene-Eocene Thermal Maximum, a hot period that occurred around 55.9 million years ago. During this roughly 170,000-year period, atmospheric carbon dioxide levels soared, temperatures rose by 5 degrees Celsius or more and ocean acidity spiked. The period ended in a hurry, geologically speaking, over the course of 30,000 to 40,000 years. Scientists are unsure what stopped the warming; possibilities include uptake of carbon by organisms or by rock.

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